Re: -mmX 4G patches feedback [numbers: how much performance impact]

[Andrea Arcangeli <andrea@suse.de>]

On Tue, Apr 06, 2004 at 01:55:39PM +0200, Ingo Molnar wrote:
> 
>         http://redhat.com/~mingo/4g-patches/loop_print.c

loop print does no memory access at all, it just loops forever, no
surprise at all you get very little slowdown no matter how many tlb
flushes happens.

If people needs >3G of user address space I assume they do some bulk
memory access too in their application.

Please write a realistic benchmark and repeat the test, the numbers you
posted are totally meaningless. Try a kernel compile of something
actually realistic (and a kernel compile doing lots of execve isn't the
worst case either).

Also note that the slowdown for app calling heavily syscalls is 30% not
5-10%, no matter if they're threaded or not, further more there has been
no proof that the 30% slowdown of mysql is really related to the
copy-users being serialized by a thread-wide spinlock, we made that
assumption but it's not certain yet.

You should also use a bleeding edge cpu for you measurements with large
tlb caches, which cpu did you use for your measurements?